Heretofore, perimeter intrusion detection systems have employed an array of seismic vibration sensors buried in the ground for detecting intruders. The output signals from the seismic sensors have been summed into a receiver and analyzed in various ways to produce an alarm indicative of an intrusion in the region being monitored. Examples of such systems can be found in the following U.S. Pat. Nos. 3,109,165 issued Oct. 29, 1963; 3,913,085 issued Oct. 14, 1975; and 4,107,660 issued Aug. 15, 1978.
While such systems are suitable for indicating an intrusion into a monitored perimeter they are not suited for indicating the location of the intrusion.
It is also known from the prior art of intrusion detection systems employing sonic sensors (microphones) to dispose microphones in a number of remote areas to be monitored. Means were provided for selectively listening to sounds made in any one or more of the remote areas in one mode and to the sum of the sounds picked up by all the microphones simultaneously in a second mode. An example of such a system is disclosed in U.S. Pat. No. 3,974,489 issued Aug. 10, 1976. While this system is suitable for monitoring a relatively small number of remote areas it is not generally suited for monitoring a perimeter having a relatively large number of sensors such as 20 or more because the operator must manually select each individual remote location when operating in the selective mode.